In the absorbent product technology, many attempts have been made to optimise the absorbent capacity and efficiency of absorbent cores by providing regions of increased or diminished basis weight and density in such cores. Also, it has been attempted to reduce leakage by providing barrier structures to the absorbent products to reduce liquid migration towards and beyond the periphery of the absorbent product.
From EP-A-052 413 it is known that for absorbent products, leakage of liquids along the waist edge can be prevented by providing a barrier sheet located between the topsheet and the backsheet and the waist ends of an absorbent article. The barrier sheet overlies the core at a waist end and prevent liquids from being squeezed out of the transverse edges of the core.
From EP-A-376 022 (Robertson) a unitary waistcap or waistband is known, wherein a unitary piece of elastomeric material extends from the perimeter of the absorbent product towards the core. The single piece of elastomeric material provides a waist elastic as well as a stand-up barrier overlying the topsheet at the waist end of the core.
From U.S. Pat. No. 4,695,278 (Lawson) an absorbent article is known comprising an elasticated stand-up barrier cuff in the leg areas.
From U.S. Pat. No. 4,795,454 (Dragoo) an absorbent article is known comprising an elasticated stand-up barrier cuff that is connected with a proximal edge to the absorbent article, and is located adjacent a gasketing cuff. A liquid-pervious topsheet terminates inboard of the proximal edge of the barrier cuff. Seal means are located along the proximal edge to prevent wicking of liquids underneath the barrier cuff.
From EP-B-0 304 631 it is known to coat and seal lateral portions of a liquid-permeable topsheet with a hot-melt adhesive to prevent lateral leakage of liquids.
In U.S. Pat. No. 4,935,022 (Lash) an absorbent structure is disclosed which has a lower storage layer and an upper acquisition/distribution layer comprising chemically stiffened cellulose fibers and absorbent gelling material. The upper acquisition/distribution layer is of larger surface area than the underlying storage layer. The lower storage layer is formed of an insert, which is placed relative to the upper acquisition/distribution layer such that about 75% of the absorbent gelling material in the lower layer is found in the front two-thirds section of the absorbent structure, and at least 55% of the total amount of absorbent gelling material is found in the front half section.
In U.S. Pat. No. 4,685,915 (Hasse) an absorbent product is disclosed having a core comprising hydrophilic fibers and absorbent gelling material, the core having an area of higher average density and basis weight than the end portions of the core. The area of higher average density and basis weight is located near the center or the front of the absorbent product.
In U.S. Pat. No. 4,834,735 (Alemany) an absorbent core is disclosed having a storage zone and an acquisition region of lower average density and basis weight than the storage zone. The core comprises a mixture of hydrophilic fibers and absorbent gelling particles. The acquisition region is located towards the front of the absorbent core.
In European Patent No EP-B-0 330 675, it is disclosed to introduce absorbent gelling material into specific locations of a horizontal, or x-y plane of an absorbent core using pulsed powder spray guns.
In International patent applications no's WO 91/11163 and WO 91/11165, a dual layer core is disclosed comprising a lower storage layer and an upper fluid acquisition/distribution layer comprising chemically stiffened cellulose fibers, the upper layer being substantially free of absorbent gelling material. The area of the acquisition/distribution layer is between 25% and 100% of the area of the lower storage layer, and is preferably of elongated shape. For adult incontinence products, the acquisition/distribution layer is generally located in the front two thirds of the absorbent article, relative to the backsheet.
In U.S. Pat. No. 4,411,660 (Dawn), an absorbent article is disclosed in which a layer consisting of absorbent gelling material underlies a fibrous layer. The layer of absorbent gelling material can be in the form of particles, fibers or a film.
In International patent application WO 91/04724, a diaper core is disclosed which linearly tapers from a relatively narrow crotch section to a relatively wide back section.
It has been observed by the applicant that especially in the category of adults suffering from incontinence, there is an increased tendency for leakage of the absorbent products when used in lying-down positions of the user. The majority of adults suffering from a severe incontinence are elderly women, for which leakage in these positions is relatively frequent compared to other users.
It is an object of the present invention to provide an absorbent product which provides reduced leakage when used in a lying down position.
It is another object of the invention to provide an absorbent article that is especially adapted for users ranging from walking infants to adults, especially women users, when confined to a predominantly lying down position.
An absorbent article according to the invention is characterised in that the average basis capacity of the absorbent material located in the back half section of the layer of absorbent material is higher than the average basis capacity of the absorbent material located in the front half section of the layer. A liquid barrier means is located between the transverse centerline of the layer and the back waist edge of the backsheet to prevent liquids from leaking to the back waist edge of the backsheet.
The average basis capacity of the absorbent core depends on the amount and on the type of absorbent material that is used in the core and is a measure for the amount of liquid that can be retained per gram of absorbent material. The average basis capacity is measured according to a test method which is based on the official method established by the German "Medizinischer Dienst der Spitzenverbande der Krankenkassen e.V." for reimbursement of incontinence absorbent products. The test method "Prufmethode Nr. 1/93 MDS-HI Teil 1, Bestimmung der Flussigkeitsaufnahme" is described in the detailed description of the invention, below.
By concentrating the absorbent material in the back half section of the absorbent article, urine is prevented from leaking from the product when used in the lying down position. As the back half section of the absorbent article is in a substantially horizontal position when used in a lying down position of the wearer, the majority of the liquids that are discharged in this position will under the influence of gravity and under influence of the weight of the user, be transported to the back half section.
When the core reaches its point of saturation, the relatively large amounts of liquids stored in the back of the absorbent core will result that liquid is squeezed out from the back transverse edge of the absorbent core. To prevent leakage of absorbed liquids from the perimeter of the core to the perimeter of the backsheet, the barrier means are located between the back transverse edge of the core and the waist transverse edge of the backsheet.
Another mechanism by which leakage can occur in the back half section, is via the topsheet of the absorbent article. To prevent leakage along the topsheet, the barrier means may be located on top of the absorbent core, in the back half section thereof. The advantage of such barrier structures is that liquids or other liquid or viscous waste is prevented from migrating along the topsheet to the back transverse edge of the absorbent core.
In one embodiment of an absorbent article according to the invention, the absorbent material may be solely comprised of hydrophilic fibers such as fluff pulp, rayon fibers or modified cellulosic fibers, or may be comprised of a foamed absorbent material as described in U.S. Pat. No. 5,268,224 (Desmarais). Applying more absorbent material of this kind in the back half section of the absorbent core can result in a so-called profiled core, which is of higher caliper in the back than in the front. Alternatively, the absorbent core is compressed to a uniform caliper, such that the density of the core is highest in the back area.
In a further embodiment of an absorbent article according to the invention, the absorbent material of the core comprises absorbent gelling material. The absorbent gelling material may be mixed with the fibrous or foamed material. Alternatively the absorbent core may be comprised of solely absorbent gelling material or may comprise layers of absorbent gelling material as described in European Application No 93309614.1.
Preferably the ratio of the average basis weight of the absorbent gelling material in the back half section and in the front half section is between 1.1 and 3, preferably between 1.2 and 3 and most preferably between 1.3 and 3.
The average basis weight of the absorbent gelling material in the front half section and in the back half section is determined by measuring the total weight of absorbent gelling material present in any one section and dividing this weight by the total area in which the absorbent gelling material is located. The weight of the absorbent gelling material is determined by separating the absorbent gelling material from the other absorbent material in any one section. The area where the absorbent gelling material is placed, is measured by applying a colouring agent to the absorbent core, such as bromocresol. The coloured areas are detected by visual inspection. Alternatively, the absorbent core may be exposed to x-rays to detect the quantity and location of the absorbent gelling material.
The barrier means may comprise a liquid-impermeable strip of material located underneath the topsheet. The strip overlies a part of the core along the back transverse edge of the core and is sealed in a liquid-tight manner to the backsheet along a sealing line.
Alternatively, the barrier means may comprise a liquid-impermeable sealing area, such as a line of connection between the topsheet and the backsheet located between the back transverse edge of the core and the back waist edge of the backsheet. The line of connection may be a glue line comprised of a single glue line, a spiral glue pattern as described in U.S. Pat. No. 4,098,632 (Sprague) or glue beads. Alternatively, the line of connection of topsheet and backsheet may be formed by fusion of the topsheet to the backsheet, for instance by crimping.
Again, alternatively, the barrier means comprises a stand-up barrier cuff having elastication means for spacing the distal edge of the cuff away from the topsheet. In again another embodiment, the barrier means comprise a section of the backsheet adjacent the back waist edge that is doubled-over to form a z-shaped fold.
The combination of the increased average basis capacity in the back half section of the absorbent core and the barrier means located in the proximity of the back waist region, make the absorbent article according to the invention especially adapted for bedridden users.